This invention relates to mechanical breathing support for patients with breathing disorders, and, more particularly, to a ventilation approach that responds to temporary discontinuance of breathing by a patient.
People breathe to rid the body of carbon dioxide and other waste products of metabolism and to supply oxygen to the body for further metabolism of food. Metabolism normally continues independently of breathing, with carbon dioxide continually being produced. Each exhalation removes the carbon dioxide accumulated since the last exhalation, so that the carbon dioxide content periodically oscillates about a normal bodily level.
Apnea is a temporary cessation of the normal breathing function experienced by some persons with breathing disorders. It is often observed in prematurely born infants whose physiological and instinctive breathing function is not fully developed. Apnea is also found in adults whose ability to control breathing is curtailed by illness, bodily deterioration, or injury.
Apnea occurs when the person, whose metabolism is functioning and who has been taking spontaneous breaths in a normal manner, suddenly stops breathing. At that point, the carbon dioxide level of the blood quickly rises, because metabolism continues and the carbon dioxide is not removed from the body by breathing. Such a rise in carbon dioxide induces a normal person to take a breath, but the person subject to apnea does not. The person's body becomes increasingly poisoned by the accumulating carbon dioxide.
A person subject to apnea who is under medical care is usually monitored and an alarm is sounded when breathing stops. One conventional response to apnea is to physically stimulate the patient, as by touching, to induce the resumption of breathing. In some instances, the person undergoing apnea is already supported on a mechanical ventilator which aids breathing under a defined procedure. Some ventilators include a built-in response to apnea, which is to provide that the patient is automatically ventilated following cessation of breathing with a series of quick mechanical breaths for some fixed period of time. This rapid ventilation reduces the carbon dioxide content of the blood to well below the normal level and increases the oxygen content to more than its normal level.
Existing assisted responses to apnea are not fully satisfactory. Physical stimulation depends upon a quick response by the therapist, does not modify the blood chemistry, and is not certain to cause the resumption of breathing. A series of quick mechanical breaths alters the blood chemistry and provides immediate relief, but does not induce the resumption of breathing.
There is a need for an improved approach to responding to a condition of apnea, which both provides immediate relief to the carbon dioxide and oxygen levels of the blood and also induces the resumption of normal breathing. The present invention fulfills this need, and provides related advantages.